Briquettes are conventionally made by agglomerating briquette filler with a binder. Briquette fillers include stock fines, such as metal fines and coal fines, minerals, fly ash or other material which may be finely divided and suitable as a briquette component. Recyclable materials such as metal scrap and organic waste, such as municipal sewage sludge, waste paper, etc. have also been used as briquette filler. Asphalt, tar-pitch, cement, starch, starch molasses, molasses, lime molasses, latex, and lignosulfonates have been used as binders in conventional briquette compositions.
U.S. Pat. No. 3,898,076 (Ranke, 1975) teaches the use of paraffin wax and a vinyl copolymer as a binder to agglomerate briquette filler. Solid organic biomass is used as a briquette filler and fly ash coke as a binder in fuel briquettes formed according to U.S. Pat. No. 4,589,887 (Aunsholt, 1986). U.S. Pat. No. 4,597,790 (Matsui et al., 1986) describes agglomerates formed from iron ore fines or iron sand as a filler with cement or granulated blast furnace slag as a binder, U.S. Pat. No. 5,221,290 (Dell, 1993) describes charcoal briquettes bound with an organic binder and a water-swellable smectite clay. U.S. Pat. No. 5,264,007 (Lask, 1993) teaches the agglomeration of caking coke and finely-divided limestone as briquette filler, using pitch and coal as a binder. U.S. Pat. No. 5,431,702 (Schulz, 1995) describes a method for making fuel briquettes using dewatered sewage sludge, and cellulosic waste such as paper as briquette filler mixed with a conventional binder.
Pitch and bituminous substances, such as asphalt, are common binding agents used in conventional processes of briquette formation, such as those described in U.S. Pat. Nos. 3,725,034 (Joseph et al., 1973); 4,698,067 (Finley et al., 1987); and 5,264,007 (Lask, 1993). Asphalt is a semisolid black substance comprising bitumen and inert matter, and is obtained as a residue of petroleum distillation. Coal-tar pitch is the residue left by the distillation of coal tar, and comprises a mixture of hydrocarbons and finely divided carbon. Coal tar pitch is also used for lowering dust levels on road surfaces, and for carbon electrodes.
The use of asphalt, coal tar pitch or petroleum pitch in a binder system in combination with lignosulfonates is known. For example, U.S. Pat. No. 4,659,374 (Alanko et al.) teaches the use of asphalt or pitch as a primary binder, and lignosulfonate salts, carbohydrates or silicates as a secondary binder in a mixed binder system for use in forming agglomerates.
Lignosulfonates can be derived from the pulping process, and contain high sulfur levels. Use of lignosulfonate, either alone or in combination with asphalt, as a briquette binder, leads to a product that may not be adequately water-proof, and is thus susceptible to degradation upon moisture absorption if, for example, exposed to rain. Thus, it is desirable to formulate a binder in which lignosulfonate levels may be reduced or eliminated, thereby lowering the sulfuir content due to lignosulfonate.
Heat curing with high heat, generally in excess of 100.degree. C., is used during conventional curing processes to strengthen the briquette. U.S. Pat. Nos. 3,725,034 (Joseph et al., 1973); 5,264,007 (Lask, 1993); and 5,302,341 (Palowitz et al., 1994), describe processes for briquette formation which include heat curing with high heat. The heat curing process provides conventional briquettes with water resistance but also adds to the expense of briquette formation. It is desirable to formulate a binder composition which does not require high heat curing for briquette formation, but which still maintains adequate water resistance.